Let's try @wil93's recommendation to whitelist packages

.travis.yml

@@ -11,6 +11,12 @@ env:
 
 addons:
   postgresql: 9.3
+  apt:
+    packages:
+    - gifsicle
+    - jpegoptim
+    - optipng
+    - jhead
 
 matrix:
   allow_failures:
@@ -32,6 +38,7 @@ sudo: false
 cache: bundler
 
 before_install:
+  - sudo apt-get install -y gifsicle jpegoptim optipng jhead
   - npm i -g eslint babel-eslint
   - eslint app/assets/javascripts
   - eslint --ext .es6 app/assets/javascripts